1. Field of the Invention
The present invention relates to a surface treatment method for an electronic part to be soldered, such as a connection terminal or a metal chassis and a surface treatment method of the same.
2. Description of the Related Art
With the control of lead for environmental protection, a lead-free product is desired, and also in the soldering work of a connection terminal indispensable for an electronic part, a demand for lead-free work is raised.
Conventionally, a connection terminal to be soldered, such as a connector or a lead frame, or a metal chassis (shell) for housing the connection terminal and the like is often subjected to, as a lead-free treatment, a surface treatment using tin with excellent solder wettability. In the case where tin is used, there has been a problem that although the solder wettability is excellent, tin whiskers are apt to be produced, and an electrical short-circuit state is apt to occur.
As an example of this kind of surface treatment method for an electronic part, for example, patent document 1 discloses that in a surface treatment method applied to a soldered area of a wiring layer of a wiring board and using a metal not containing tin, plating using an electroless method is performed on the wiring layer by means of three layers of a nickel layer with an average particle size of 20 nm or more and of 0.5 μm to 5 μm thickness, a palladium or palladium alloy layer of 0.005 μm to 2 μm thickness, and a gold layer of 0.05 μm to 0.8 μm thickness.
[Patent document 1] JP-A-2002-111188 (pages 3 to 5, FIG. 2)
However, as an electronic part to be soldered, such as a connection terminal or a metal chassis, there is desired one which is lead-free, has no whisker, has excellent solder wettability, has excellent corrosion resistance, uses a small amount of gold, and has excellent plating productivity.
In the treatment method of patent document 1, the amount of usage of gold is large, the plating productivity is not excellent, and there is a tendency that cost becomes high. Besides, since the amount of usage of gold is large, there has also been a problem that at the time of soldering of a recent fine pitch product, the concentration of gold in the solder becomes high, and solder strength is lowered.